Patent EP-0 296 974, in the name of the Applicant describes resilient supports providing a large amount of clearance for protecting electronic equipment from shock, in particular in the event of a collision or of an explosion. In a variant embodiment described in that patent, the support includes an elastomer arm having a plurality of cables of composite material embedded therein and extended along one side by fastening means that form circular or elliptical arcs including two spring blades of composite material connected together by a layer of elastomer. The elastomer arm including composite cables is connected to the circular or elliptical arc-forming fastening device by a transition zone enabling thickness and width to vary continuously. The arm made of natural rubber which has a low damping coefficient is thicker and narrower than the fastening device which is made of an elastomer that has a high damping coefficient.
The resilient support of patent EP-0 296 974 does not provide effective filtering of vibration, particularly vibration at a frequency lying in the range 10 Hz to 800 Hz. The bottom spring blade is directly secured to a metal fixing support which enhances vibration propagation.
At no moment does that document describe damping vibration by shear in the layer of elastomer lying between the two spring blades made of composite material. On the contrary, the assembly constituted by the spring blades and the intermediate elastomer layer is referred to in column 14, line 39, as "a matrix-fixing composite spring". Furthermore, in column 14, lines 4 to 6, the possibility is suggested of implementing a fixing device that includes a central layer of composite material with two extreme layers of elastomer. In that variant embodiment, the shear required for damping vibration is not achieved.
Also, the blade springs extend within the resilient support of patent EP-0 296 974 only as far as the transition zone between the arms and the fastening means that form a circular arc, and that does not provide the stiffness and resonant frequency characteristics suitable for filtering vibration.
U.S. Pat. No. 4,942,075 describes a spring comprising two oval blades between which a layer of rubber is interposed. In FIG. 4 of that patent, there can be seen an embodiment in which the layer of rubber does not extend in the arcuate zones.
EP-A-0 132 048 describes a spring having mutually parallel blades between which a layer of elastomer is interposed for damping purposes. The embodiment shown in FIG. 11 of that document includes an outer layer 32 of elastomer which does not contribute to damping vibration.
Those patents do not disclose, nor do they suggest, implementing shear forces within rubber for the purpose of damping vibration.